Abstract
Measurements are presented by the CMS Collaboration at the Large Hadron Collider (LHC) of the higher-order harmonic coefficients that describe the azimuthal anisotropy of charged particles emitted in sqrt(s[NN]) = 2.76 TeV PbPb collisions. Expressed in terms of the Fourier components of the azimuthal distribution, the n = 3-6 harmonic coefficients are presented for charged particles as a function of their transverse momentum (0.3 < pt < 8.0 GeV), collision centrality (0-70%), and pseudorapidity (abs(eta) < 2.0). The data are analyzed using the event plane, multiparticle cumulant, and Lee-Yang zeros methods, which provide different sensitivities to initial-state fluctuations. Taken together with earlier LHC measurements of elliptic flow (n = 2), the results on higher-order harmonic coefficients develop a more complete picture of the collective motion in high-energy heavy-ion collisions and shed light on the properties of the produced medium.
Highlights
In the collision of two heavy ions moving relativistically, a high-density energetic state of matter is created in the overlap region of the two Lorentz-contracted nuclei
Earlier studies at the Relativistic Heavy-Ion Collider (RHIC), where gold nuclei wtoe√rescNoNll=ide2d00atGneuVcl[e1o–n4-n],ufcoleuonnd center-of-mass energies up that the particles produced in rare, high-momentum-transfer scatterings encounter a dense medium with high stopping power for colored probes
Pressure gradients that develop in the fluid during the collision result in an anisotropic momentum distribution of the outflowing matter, which, in turn, leads to a preferential emission of particles in the short direction of the lenticular-shaped overlap region [10,11,12]
Summary
In the collision of two heavy ions moving relativistically, a high-density energetic state of matter is created in the overlap region of the two Lorentz-contracted nuclei. The low-momentum particles that comprise the bulk of the medium exhibit strong azimuthal anisotropies that indicate a collective fluid expansion. These findings have been interpreted as manifestations of a strongly interacting quark-gluon plasma. Pressure gradients that develop in the fluid during the collision result in an anisotropic momentum distribution of the outflowing matter, which, in turn, leads to a preferential emission of particles in the short direction of the lenticular-shaped overlap region [10,11,12]. The anisotropy depends on the initial conditions, allowing the investigation of whether a Glauber-like picture of individual nucleon collisions [13]
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